[PATCH RFCv2 1/1] Introduce VCPUOP_reset_vcpu_info

[Vitaly Kuznetsov <vkuznets@redhat.com>]

When an SMP guest performs kexec/kdump it tries issuing VCPUOP_register_vcpu_info.
This fails due to vcpu_info already being registered. Introduce new vcpu operation
to reset vcpu_info to its default state.

Based on the original patch by Konrad Rzeszutek Wilk.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes from RFCv1:
- Don't use unsuitable unmap_vcpu_info(), rewrite [Jan Beulich]
- Require FIFO ABI being in 2-level mode
- Describe limitations in include/public/vcpu.h [Jan Beulich]
---
 xen/arch/x86/hvm/hvm.c    |  1 +
 xen/common/domain.c       | 61 +++++++++++++++++++++++++++++++++++++++++++++++
 xen/include/public/vcpu.h | 14 +++++++++++
 3 files changed, 76 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 216c3f2..7917272 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3332,6 +3332,7 @@ static long hvm_vcpu_op(
     case VCPUOP_set_singleshot_timer:
     case VCPUOP_stop_singleshot_timer:
     case VCPUOP_register_vcpu_info:
+    case VCPUOP_reset_vcpu_info:
     case VCPUOP_register_vcpu_time_memory_area:
         rc = do_vcpu_op(cmd, vcpuid, arg);
         break;
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 44e5cbe..889c313 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1116,6 +1116,67 @@ long do_vcpu_op(int cmd, int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
     }
 
+    case VCPUOP_reset_vcpu_info:
+    {
+        vcpu_info_t *old_info;
+        unsigned int i;
+
+        if ( !test_bit(_VPF_down, &v->pause_flags) )
+        {
+            printk(XENLOG_G_WARNING
+                   "%pv: VCPU is up, refusing to reset vcpu_info!\n", v);
+            return -EBUSY;
+        }
+
+        if ( v->evtchn_fifo )
+        {
+            printk(XENLOG_G_WARNING "%pv: FIFO evtchn ABI is being used,"
+                   "refusing to reset vcpu_info!\n", v);
+            return -EBUSY;
+        }
+
+        if ( v->vcpu_info_mfn == INVALID_MFN )
+        {
+            rc = 0;
+            break;
+        }
+
+        domain_lock(d);
+        old_info = v->vcpu_info;
+
+        if ( vcpuid < XEN_LEGACY_MAX_VCPUS )
+        {
+            memcpy(&shared_info(d, vcpu_info[vcpuid]), v->vcpu_info,
+                   sizeof(vcpu_info_t));
+            v->vcpu_info = (vcpu_info_t *)&shared_info(d, vcpu_info[vcpuid]);
+        }
+        else
+        {
+            v->vcpu_info = &dummy_vcpu_info;
+        }
+        unmap_domain_page_global((void *)
+                                 ((unsigned long)old_info & PAGE_MASK));
+
+        put_page_and_type(mfn_to_page(v->vcpu_info_mfn));
+        v->vcpu_info_mfn = INVALID_MFN;
+
+        /* Make sure vcpu_info was set */
+        smp_wmb();
+
+        if ( vcpuid < XEN_LEGACY_MAX_VCPUS )
+        {
+            /*
+             * Mark everything as being pending to make sure nothing gets lost.
+             */
+            vcpu_info(v, evtchn_upcall_pending) = 1;
+            for ( i = 0; i < BITS_PER_EVTCHN_WORD(d); i++ )
+                set_bit(i, &vcpu_info(v, evtchn_pending_sel));
+        }
+        domain_unlock(d);
+        rc = 0;
+        break;
+    }
+
     case VCPUOP_register_runstate_memory_area:
     {
         struct vcpu_register_runstate_memory_area area;
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index e888daf..81bc1b9 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -227,6 +227,20 @@ struct vcpu_register_time_memory_area {
 typedef struct vcpu_register_time_memory_area vcpu_register_time_memory_area_t;
 DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t);
 
+/*
+ * Reset all of the vcpu_info information from their previous location
+ * to the default one used at bootup. The following prerequisites should be met:
+ *  1. VCPU should be switched off. This means the operation is unsupported for
+ *     boot VCPU.
+ *  2. Domain should not be using FIFO-based event channel ABI. In case it is in
+ *     use domain is supposed to switch back to 2-level ABI with EVTCHNOP_reset.
+ *
+ * After the call vcpu_info is reset to its default state: first
+ * XEN_LEGACY_MAX_VCPUS VCPUs will get it switched to shared_info and all other
+ * VCPUs will get dummy_vcpu_info.
+ */
+#define VCPUOP_reset_vcpu_info   14
+
 #endif /* __XEN_PUBLIC_VCPU_H__ */
 
 /*
-- 
1.9.3